Such feed pumps are used, for example, for pumping cooling water. These pumps are classified as wet-rotor motors in which the rotors are in contact with the pumped liquid and a distinction is made between stator windings which are in contact with the pumped liquid (wet stator windings) and those which are not (dry stator windings). A wet stator winding can operate at high current levels because it is cooled by the pumped liquid.
It has been found, however, that if the rotor is contacted with the pumped liquid, large losses due to liquid turbulence are produced.
German patent DE 43 04 149 C1 discloses a liquid feed pump in which a rotor compartment and a stator compartment are hermetically sealed from a cooling compartment through which liquid is flowing. As a result the bearings of the rotor in the rotor compartment are not adequately lubricated